There’s plenty of evidence that lack of sleep puts you at higher risk of gaining weight. A new Swedish study in the Journal of Clinicla Endocrinology and Metabolism (press release here, abstract here) offers some new insights with fMRI brain scans:

We already know that obese people tend to find food more rewarding, as indicated by brain scans of activity in the anterior cingulate cortex:

Higher activation of this brain region has been found in obese compared with normal-weight subjects when anticipating food, suggesting that the rewarding quality of food is enhanced in obesity.

The study took a dozen volunteers and kept them up all night, then looked at their brain’s response to images of food. Compared to after a normal night of sleep, they observed the same changes that you see in obesity: stronger activation of the ACC, indicating higher dopamine signalling. You want more food than normal, because food makes you feel better than it normally would. As the graph on the right shows, those with the biggest changes in brain activity also reported the biggest appetite.

A study like this, where the subjects stayed up all night, isn’t a great way of figuring out what happens in the much more common situation of, say, getting half an hour less sleep than you need, night after night for weeks or months on end. But other studies looking at appetite hormones like ghrelin and leptin suggest that the effects are similar: too little sleep = greater appetite relative to energy needs.

Of course, this leaves us with a riddle: if you have to get up an hour early to fit your workout in, do the benefits outweigh the downsides? That depends on a lot of things, but my general sense is that exercise has so many benefits that it’s still worthwhile. The real answer, of course, is to organize your life so that you can sleep enough and get some exercise.

I didn’t read the full article, but I wonder whether the authors considered a connection with the antidepressant/hypomania-inducing effect of one night’s total sleep deprivation. Increased reward response would seem to be in line with this. On the other hand, most chronically sleep-deprived people would tell you that chronic sleep deprivation doesn’t have such an antidepressant-like effect, but rather, makes you want to eat (especially carbs) because you feel like you need the energy. How this ties in with appetite hormones, I couldn’t say offhand. So it’s interesting, and it’s possible that this study is relevant to weight gain with chronic sleep deprivation, but I would suspect that there might be different mechanisms at work.

@Anthony: Yes, that could certainly be a way of looking at it evolutionarily. Of course, we could probably also come up with a reason that evolution would make us eat LESS during sleep deprivation. 🙂 It may simply be that effects like this aren’t the result of direct selection, but are just byproducts of the fact that the brain uses the same circuitry to respond to different stimuli, so there can be unintended cross-talk between inputs.

@Todd: That’s an interesting question. I guess many of our behaviours could be looked at as controlled by a balance between inhibition (affected by ego depletion) and impulse (reward seeking) — but it’s likely that the two are highly intertwined.

@Anna: Yes, I think you’re right that a full night of sleep deprivation is quite different than chronic sleep shortage — I probably should have emphasized that more in the blog entry. The researchers suggest that this particular study may be relevant to shift workers, who have to totally disrupt sleep patterns.

@Mélanie: Yes, that’s definitely a possibility (they cite an earlier study suggesting that energy expenditure is 7% higher when you’re awake for the night). On the other hand, they measured fasting plasma glucose levels in the morning and found no difference.

Well, I do think the lack of sleep can put you at risk of gaining weight. I have personally observed a couple of workplaces where people work in night shifts. I think though that night shift workers often experience weight gain. That is often what I have heard from them as well.